juice indicator
Grape juice turns red when an acid is added to it. It will
turn green when a base is added.
Mix 1 part grape juice to 9 parts water. Pour some of the
solution into a glass which has several drops of household
ammonia already in it. Since the ammonia is a base the juice
turns green. Pour this green liquid into a third glass which
already has a tablespoon of vinegar in it. It will turn red.
Vinegar is an acid.
Another liquid that acts the same way can be made from purple
cabbage. Chop the leaves, boil them in a small amount of water
and pour through a strainer to remove the leaves.
Two other common acids are lemon and grapefruit juice. Two
other bases are baking soda and cream of tartar.
Ammonia is poisonous. If you put ammonia in a glass used for
drinking, wash the glass thoroughly when you are done with it.